Continuously variable inductance device



Oct. 12, 1-943. v VANCE V 2,331,522

CONTINUOUSLY VARIABLE INDUCTANCE DEVICE Filed Sept. :50, 194i- 2 Sheets-Sheet 1 3nventor DONALD H.\/ANCE attorneg Oct. 12, 1943. D V N 2,331,522

CONTINUOUSLY VARIABLE INDUCTANCE DEVICE inventor DONALD H.VANCE BB W (Ittotneg Patented Oct. 12, 1943 UNITED STATES PATENT-"OFFICE CONTINUOUSLY, VARIABLE INDUCTANCE DEVICE Donald H. Vance, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application September 30, 1941, Serial No. 413,068

3 Claims. (Cl. 171-242) to provide a simple and trouble-free means for detuning the unused portions of the variable inductor of a tank circuit, by shorting it in a number of places to prevent power-absorbing parallel resonance, within the desired frequency band.

The foregoing and other'obiects are achieved in accordance with the invention by the combination with a space wound coil of a plurality of tap means movably mounted in short-circuiting relation with respect to different turns of said coil, and means for simultaneously moving said tap means at different rates along the said coil.

Certain details of construction together with other objects and advantages will be apparent and the invention itself will be best understood by reference to the following specification and to the accompanying drawings, wherein Figure 1 is a top plan view of a continuously variable inductor which is provided, in accordance with the invention, with a plurality of continuously and relatively movable taps or trolleys,

Figure 2 is a trahsverse'sectional view taken on the line 2-2 of Fig. 1,

Figure 3 is a circuit diagram which will be referred to in explaining the electrical connections for the device of Fi 1,

Figure 4 is a fragmentary sectional view taken on the line 4-4 of Fig. 2 showing the details of a preferred form of trolley.

In the drawings, wherein like reference characters designate the same or corresponding parts in all views, I designates generally a chassis or frame having a front and rear insulating panel 2 and 3, respectively, which aremalntained in spaced rigid relationship by a pair ofthreaded metal rods l and 5 which are fixed to the panels adjacent their base, and a third preferably unthreaded metal rod 6, which is centrally disposed between the two panels adjacent the top of'the frame. v

Journalled for rotation in bushings 'l and 8 inthe panels 2 and 3 are two metal stub shafts 8 and 19, respectively, which support a coil form indicated generally at H (Fig. 2). This coil form may comprise a front and a rear group of four bifurcated arms l2, l3, respectively. which extend radially from the stub shafts 9 and it ,upon which they are respectively mounted. The arms i2 and [3 are aligned one with the other and each pair of arms supports an insulating spacer bar It whichis clamped rigidly in the bifurcated ends by bolts 15. Each spacer arm is provided with lateral grooves i6 (see Fig. l) on its exposed outer surface in which a wire or rlb-. lion-like conductor i1 is spirally wound, edgewise. -The opposite ends of this coil are fixed, as at l8, '19, respectively, to the oppositely located bifurcated sets of crossed arms I! and I3. The

coil form has an axis of rotation which coincides with the common axis of the stub shafts 9 and I0 and may be rotated thereabout as by means of an insulatingpontrol knob 20 which is fixed on an extension 9a of the stub shaft at the front of the chassis.

Since the cross arms 12 and I3 are of metal and are supported on the metal stub shafts 8 and I9 which are journalled for rotation in the metal bushings I and 8, it is apparent that electrical connections may be made to the exterior of the panels 2 and 3, irrespective of the setting or angle of rotation of the coil form.' Such electric connections are conveniently established by means of metal strips 2| and 22 which extend along the opposite faces of the front and rearpanels to the binding posts 23 and 24, respectively. For a purpose later described, an additional strip or wire 25 is provided adjacent the rear surface of panel 3 for connecting the rods or shaft l, 5 and 6 to the binding post 24. Thus, as in standard practice, a tap in the form of a grooved trolley wheel 26 which is mounted for slidable movement on the upper central rod 5 serves to variably adjust the electrically eifec tive number of turns of the coil 11 upon rotation of the control knob 20. Thus, when the control knob 20 is rotated, the coil rotates in contact with the trolley 26 and, since the coil is spiralwound, the said tap or wheel will be moved along the rod 5 in a direction determined by the direction of rotation of the coil. Thus, a maximum value of inductance may be achieved when the wheel 25 is moved to the rear of the coil and a minimum value of inductance when this wheel is at the front end of the coil. In order to halt the movement of the coil 11 when the wheel 28 reaches the ends of the coil, a stop 21 is provided on each of the sets of cross arms I: and 13. As shown more clearly in Fig. 2 (which shows the rear stop 21), each stop may be in the form of a rigid metal strip fixed to the side of one of the met the coil support, and which extends radially therebeyond. Thus, when the wheel 28 means (hereinafter described), that'portion of the cell which at any given moment is unused may absorb power from. that portion of the coil which is in circuit and in certain cases (depending upon the electrical constants of the unused portion of the coil) set up disturbing electrical fields. To obviate this diillculty, the present invention provides a pair of auxiliary taps or trolleys" and 29 which are mounted upon the rods. 4 and 5, respectively, in' contact with different trailing turns of the coil. The treads of the wheels 28 and are preferably wide enough to.

contact more than one turn of the coil.

thereon, are-provided, with threads of different pitch. The pitch of these. threads is preferably, but not necessarily, so calculated that these-auxiliary trolleys, 28, 29, advance, respectively, twothirds' and one-third the number of turns the main trolley 23 advances. Since, as previously set forth, the rods orshafts I, S and 6 upon which the trolleys 28, 28 and." advance are electrically connected by the wire or wires 25 to the-common binding post 2|, the unused portion b (see F18. 3) of the coil I1 is broken up or detuned" by the auxiliary taps 28 and 29 into small sections bl, b2 andbt of very high (and hence undisturbing) self-resonant frequencies. This permits the design of a rotary inductance coil for use at low frequencies and over a wide range without disturbing power absorption due to so-called back-end resonance.

'able to employ a form of trolley incorporating a apringor the like for compensating for such eccentricity. '1he compensated trolley wheel 2! shown in section in Fig. 445 claimed in copendins application Serial No. 391,164, to Charles T.

a conically tapered head 34 which extends out-.

wardly therefrom at an angle with respect to the head 31 on the hub 20. The rim 2! which con- The rods I and 5,, and the hubs of trolleys 28, 29

provided on the one side with a conically tapered surface 31 which rides on-the complementa'rily tapered surface 34 on the head of the sleeve 33. The tread 35 and the surface of the coil l'l against which it bears are preferably knurled, as indi cated at k, to reduce or obviate slippage therebetween.

A coiled spring 38 arranged about the sleeve 33 and which is anchored adjacent the bearing. and of the hub 30 exerts its force against the head of the sleeve and causes the tapered surface 24 thereon to bear against the tapered surface I! of the rim 35. This serves to center the rim with respect to the axis of movement of the hub 30 and, in the event that the tread encounters any eccentricity in the rotation of the coil ll about its axis, permits the rim 35 to be rotated ofl its normal center as long as the eccentricity is en-- countered. Where, as in the instant case, the spring 38 is constituted of steel, it is preferable to shield the spring from radio'frequency voltthose skilled in the art. It will be understood,'

therefore, that the foregoing description of a presently preferred embodiment of'the invention .a plurality of conductive shafts extending. axially of said coil and electrically connected one to the other, a tap mounted for longitudinal movement upon one of said shafts and arranged to be moved therealong in contact with said coil at a certain rate, a second tap mounted for longitudinal movement upon another of.aa.id shafts and arranged to be moved therealong-in contact with said coil at a different rate, and means for simultaneously moving said taps along their respective shafts at said different rates.

2. The invention as set forth in claim .1 and wherein three shafts and three taps are employed, and wherein the rate at which one of said taps is moved along said coil is twice the rate of another tap and the rate at which said third Cole, Jr., filed April 30, 194i, and comprises a hub tap is moved along said coil is three times that 4 of said second-mentioned tap.

. tacts thecoil-ll is mounted in the space between the hub-head SI and the sleeve head 84, and is 3. In combination; an inductance coil, a plurality of tap means. mounted for movement in contact with saidicoil, andmeans for simultaneously moving said tap means along said coil in the same direction and at different rates whereby said coil is at all times effectively divided into a plurality of sections of different values of. in-

ductance.

. l DONALD H. VANCE. 

